In an Electric Power Steering (xe2x80x9cEPSxe2x80x9d) system, it may be desirable to provide the absolute hand-wheel position. This position may be used, for example, to cause the hand-wheel to return to center following a steering input. The return to center effect simulates the self-aligning torque due to positive caster of a conventional manual steering system, and causes the vehicle to be more comfortably controlled by a driver. To determine the center, absolute hand-wheel position information may be used. Typically, the absolute hand-wheel position is derived using a dual triangular wave (xe2x80x9cDTWxe2x80x9d) sensor to provide two position signals from which the relative position within 360 hand-wheel degrees is obtained. This information is then used by typically complex algorithms to determine the absolute hand-wheel position. A function of the algorithms is to provide the revolution offset or the xe2x80x9cturnxe2x80x9d at which the hand-wheel is currently positioned.
To perform this task, typical algorithms may make use of torque signals and relative position signals to estimate the driving conditions and vehicle dynamics, require the hand-wheel to have moved through a certain travel to produce a travel exclusion signal, and/or use a previous position signal that is retrieved from a microprocessor memory.
The above described and other features are exemplified by the following Figures and Description in which an absolute hand-wheel position tracking system for an electric power steering system having a hand-wheel, an assist motor for providing an assist torque disposed relative to the hand-wheel, and a motor position sensor responsive to the assist motor, includes a hand-wheel position initialization function responsive to the hand-wheel; a motor position correction and scaling function responsive to the motor position sensor and responsive to the assist torque; an enable function responsive to the assist torque and responsive to the hand-wheel position initialization function; and an absolute hand-wheel position generation function in signal communication with the hand-wheel position initialization function, the motor position correction and scaling function, and the enable function.